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Anaesthesia > Day 3: General Anaesthetic Agents: Intravenous > Flashcards

Day 3: General Anaesthetic Agents: Intravenous Flashcards

1
Q

What role do induction agents play in anesthesia?

A

Induction agents initiate anesthesia by producing loss of consciousness.

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2
Q

How quickly do true IV induction agents produce loss of consciousness?

A

True IV induction agents typically produce loss of consciousness within one arm-brain circulation time, approximately 30 seconds.

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3
Q

What is the approximate duration of action for a single dose of an induction agent?

A

A single dose of an induction agent wears off after a few minutes

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4
Q

Why is maintenance anesthesia necessary after induction?

A

Maintenance anesthesia is required to sustain the anesthetic state throughout the procedure.

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5
Q

What is the significance of the arm-brain circulation time in relation to induction agents?

A

Arm-brain circulation time is significant as it represents the time it takes for a drug administered intravenously to reach the brain and induce anesthesia.

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6
Q

classification of agents

A

-rapidly acting “true induction agents”
- slower acting

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7
Q

rapidly acting

A

Thiopentone
Etomidate
Propofol
Ketamine

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8
Q

slower acting

A

Benzodiazepines (midazolam)
Neuroleptic-anaesthetics
Opioids (in large doses)

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9
Q

advantages of IV induction

A

-Rapid onset of action
-More pleasant & acceptable for the patient
-Pollution free
-Low incidence of side-effects
-Smooth induction with rapid transfer through the classic stages of anaesthesia

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10
Q

disadvantages of IV induction

A

-Requires intravenous access
-It is easy to give too much …. side-effects
-No removal of drug via the lungs as with inhalational
-Recovery requires
*Redistribution
*Metabolism
*Excretion
-Sudden loss of normal protective reflexes

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11
Q

mechanism of action

A

-Most sedative hypnotics exert their effect via the inhibitory GABAA receptors
*GABA – γ (gamma)-aminobutyric acid
*Increased chloride conductance → hyperpolarisation → neuronal inhibition
-Some inhibit the release of glutamate, an excitatory amino acid, in brain

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12
Q

what is pharmacokinetics

A

Pharmacokinetics refers to the processes by which a drug is:
-Taken up by the body (absorption)
-Distributed to various tissues (distribution)
-Metabolised (usually via the liver)
-Excreted (e.g kidneys, GIT)

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13
Q

pharmacodynamics

A

Pharmacodynamics refers to the drug’s effects on the body

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14
Q

What factors influence the onset of action of intravenous anesthetics?

A

The onset of action of intravenous anesthetics depends on factors such as
-speed of injection,
-lipid solubility,
-protein binding, and
-blood flow to the brain.

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15
Q

What is the significance of the arm-brain circulation time in pharmacokinetics?

A

Arm-brain circulation time is crucial as it represents the time it takes for the drug to reach the effect site (the brain) by crossing the Blood-Brain Barrier.

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16
Q

How does recovery from intravenous anesthesia occur?

A

Recovery from intravenous anesthesia involves redistribution from vessel-rich to vessel-poor organs, metabolism, and excretion.

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17
Q

What processes contribute to the redistribution of intravenous anesthetics from vessel-rich to vessel-poor organs?

A

Intravenous anesthetics redistribute from the brain to other tissues, such as muscles, as anesthesia wanes.

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18
Q

How are intravenous anesthetics metabolized and excreted from the body during recovery?

A

Metabolism and excretion processes remove intravenous anesthetics from the body, contributing to recovery.

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19
Q

What is redistribution in the context of intravenous anesthesia?

A

Redistribution refers to the movement of intravenous anesthetic drugs from the brain to other less well-perfused tissues in the body.

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20
Q

How does redistribution contribute to the patient waking up after IV induction?

A

After IV induction, the patient wakes up due to redistribution, as the drug moves away from the brain.

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21
Q

Why does rapid awakening occur after redistribution?

A

Rapid awakening occurs because low concentrations of the drug remain in the brain, impairing concentration and higher functioning.

rapid awakening is not because of metabolism or excretion

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22
Q

What effect does the low concentration of the drug remaining in the brain have on the patient?

A

The low concentration of the drug in the brain post-redistribution can impair cognitive functions.

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23
Q

What precautions are recommended regarding driving and decision-making post-anaesthesia?

A

Patients are advised not to drive or make important decisions for 48-72 hours post-anaesthesia due to these effects.

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24
Q

the ideal IV induction agent

A

-smooth and rapid onset of action
-inexpensive
-rapid recovery
-minimal side effects/ toxicity
-no pain on injection

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25
Q

practical points with IV induction

A

Reduce pain on injection
-IV lignocaine 10-20mg in syringe when giving propofol
-New, large-bore, free-running IV line

Titrate to effect….. You can always give more

Less in elderly …. More in children

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26
Q

ketamine

A

unique: dissociative anaesthetic and analgesic

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27
Q

The international colour coding for all true IV induction agents is

A

yellow

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28
Q

The international colour coding for IV sedatives is

A

orange

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29
Q

What is the chemical composition of propofol?

A

Propofol’s chemical name is 2,6 di-isopropylphenol.

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30
Q

How is propofol prepared for administration due to its lack of solubility in water?

A

Propofol is prepared as an emulsion due to its insolubility in water.

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31
Q

What components are used to prepare propofol as an emulsion?

A

The components used to prepare propofol as an emulsion include soya bean oil, egg phosphatide (egg yolk), and glycerol.

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32
Q

What are the concerns regarding the use of fat emulsion in propofol?

A

Concerns regarding the use of fat emulsion in propofol include its potential as a culture medium for microorganisms.

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33
Q

What are the recommended guidelines for the use of propofol regarding its shelf life and administration?

A

Propofol should be used within 6 hours of opening.

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34
Q

What are the available sizes and concentrations of propofol ampoules?

A

Multiple ampoule sizes are available, including 20ml, 50ml, or 100ml, with concentrations of 1% or 2% (1% equals 10mg/ml).

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35
Q

What is the lipid solubility of propofol?

A

Propofol is extremely lipid-soluble.

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36
Q

How does propofol interact with the blood-brain barrier?

A

Propofol easily crosses the blood-brain barrier.

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37
Q

What type of metabolism does propofol undergo, and how does it contribute to rapid plasma clearance?

A

Propofol undergoes extra-hepatic metabolism, leading to rapid plasma clearance and emergence.

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38
Q

What are the versatile uses of propofol in anesthesia?

A

Propofol is versatile and can be used for
-induction,
-maintenance (Total Intravenous Anaesthetic - TIVA), and
-sedation in lower doses.

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39
Q

propofol: induction doses

A

Adults: 2 – 2.5 mg/kg

Elderly: 1 – 1.5 mg/kg

Children: 2.5 – 3 mg/kg

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40
Q

propofol: organ effects

A

CNS
CVS
Respiratory
GIT
Metabolic

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41
Q

propofol: CNS effects

A

Rapid LOC + recovery

Less hangover effect than other induction agents or gases

No real excitatory effects

Very slight analgesic effect

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42
Q

propofol: CVS effects

A

-Dose-dependent cardiovascular depression
-↓ Systemic Vascular Resistance (SVR)
-↓ BP
-Slight ↑ HR
-Large doses administered rapidly significantly depress the CVS vs. small doses administered slowly
-Careful in elderly and fluid-depleted patients
- Not suitable in shock / haemorrhage / significant CVS compromise

43
Q

Propofol: Respiratory effects

A

-Dose-dependent depression
-Apnoea on induction close to 100%
-Inhibits laryngeal reflexes
-No histamine release

44
Q

Propofol: other effects

A

-Anti-emetic  useful in patients with PONV
-Propofol Infusion Syndrome (PRIS)
*Seen with prolonged high-dose infusions
*Presents with lipaemia, metabolic acidosis, myopathy
*May be fatal

45
Q

Propofol: Ideal for these specific scenarios

A

TIVA
Conscious sedation
Asthma
Porphyria
History of PONV
History of Malignant Hyperthermia

46
Q

What is a major concern associated with propofol administration?

A

Cardiovascular depression is a major concern with propofol.

47
Q

In which patient populations should caution be exercised when administering propofol?

A

Elderly
Cardiac failure
Hypovolaemia
Fixed cardiac output
–Aortic / Mitral stenosis
–HOCM

48
Q

What is the most common use of propofol in anesthesia?

A

Propofol is most commonly used as an intravenous induction agent in anesthesia.

49
Q

What physical form does thiopentone typically have?

A

Thiopentone typically exists as a yellow powder.

50
Q

How is thiopentone typically prepared for use?

A

Thiopentone is usually mixed with water or normal saline for administration.

51
Q

What is the pH of thiopentone solution?

A

The pH of thiopentone solution is 10.5.

52
Q

How long is thiopentone solution stable for?

A

Thiopentone solution is stable for 24-48 hours.

53
Q

induction dose of thiopentone

A

Adults: 3 – 5mg/kg
Children: 5-6mg/kg
Caution in elderly

54
Q

thiopentone: CNS effects

A

-LOC in 30 sec
*Classically described for Rapid Sequence Induction
-Smooth, no reflex movements or coughing
-Antanalgesic  may LOWER pain threshold
-Anti-convulsant
-Used in treatment of STATUS EPILEPTICUS
-Neuroprotective
*↓CMRO2
*↓ ICP

55
Q

Thiopentone: CVS effects

A

↓ Cardiac output (10–20%)
-Vasodilatation
-Negative inotropy
-↓ central catecholamine release

Compensatory ↑HR

Exaggerated response with
-Elderly
-Cardiac failure
-Fixed cardiac output
-Hypovolaemia

56
Q

Thiopentone: Respiratory effects

A

-Dose-dependent apnoea
0No depression of laryngeal reflexes
-Histamine release: careful in asthmatics

57
Q

thiopentone: other effects

A

-Irritant to tissues
*Venous thrombosis with older 5% solutions

-Intra-arterial injection is a disaster
*Precipitation of solid crystals of thiopentone in arteries due to blood pH of 7.4
*Acute ischaemia of limb

-No specific concerns with regards to renal, hepatic or GIT side-effects

58
Q

Thiopentone: Contraindications

A

Absolute:
-Porphyria
-Known allergy (rare)

Relative:
-Asthma
-Cardiovascular instability

59
Q

What are the typical physical properties of etomidate?

A

Etomidate typically exists as a clear solution with propylene glycol.

60
Q

In what form is etomidate commonly available (ampoule size and concentration)?

A

It is commonly available in 10 ml ampoules with a concentration of 2 mg/ml, resulting in 20 mg in each ampoule

61
Q

Describe the appearance of etomidate solutions.

A

Etomidate solutions can appear as either a clear solution or an opaque white emulsion, similar to propofol.

62
Q

What is a notable characteristic of etomidate solutions upon injection?

A

Both forms of etomidate solutions are known to cause pain upon injection.

63
Q

etomidate dose

A

0.2–03 mg/kg (Adult: typically 16-20 mg)

64
Q

What is the typical duration of recovery after administering etomidate?

A

Etomidate typically leads to rapid recovery within 6-8 minutes after administration.

65
Q

Is the effect of repeated doses cumulative?

A

Repeated doses of etomidate do not result in cumulative effects.

66
Q

Why is etomidate not suitable for infusion?

A

Etomidate is not suitable for infusion due to its potential for causing adrenocortical suppression.

67
Q

For what purpose is etomidate primarily used?

A

Etomidate is primarily used for induction of anesthesia and is not intended for continuous infusion.

68
Q

etomidate: CNS

A

-Rapid LOC
-Myoclonus and involuntary movements
*Reduced by concurrent opiate and benzodiazepine use

69
Q

etomidate: CVS

A

Most stable
Little change in BP or HR

70
Q

etomidate: respiratory

A

Minimal respiratory depression
No histamine release
Least likely to cause anaphylaxis

71
Q

etomidate: GIT

A

Severe PONV!
“VOMIDATE”

72
Q

etomidate: endocrine

A

Inhibition of steroid synthesis (cortisol & aldosterone)

73
Q

What are the typical concentrations of ketamine available in solutions?

A

Ketamine is available in solutions of 1% (10mg/ml) and 10% (100mg/ml).

74
Q

Is ketamine typically stored in single-use vials or multi-use vials?

A

Ketamine is commonly stored in multi-use vials.

75
Q

What type of receptor does ketamine antagonize?

A

Ketamine antagonizes the NMDA receptor.

76
Q

Does ketamine cause pain upon injection?

A

Ketamine typically does not cause pain upon injection.

77
Q

Besides inducing loss of consciousness, what other effect does ketamine have?

A

Ketamine acts as a potent analgesic in addition to inducing loss of consciousness.

78
Q

In what routes can ketamine be administered?

A

Ketamine can be administered intravenously (IV), intramuscularly (IM), and even orally.

79
Q

ketamine: CNS effects

A

-Phencyclidine derivative
-Dissociative anaesthetic
-Complete analgesia
-↑ ICP and IOP
-Psychiatric reactions:
*Hallucinations and emergence delirium
*Less in children, males, elderly and repeated administration
*Worse if patient stimulated on awakening

80
Q

ketamine: CVS effects

A

-CENTRAL sympathetic stimulant
↑ HR
↑ BP
↑ C.O.
↑ SVR

-But… direct myocardial depressant
-Not arrhythmogenic

81
Q

ketamine: respiratory effects

A

-Minimal or no respiratory depression
-Preserved pharyngeal reflexes
-Maintains airway
*Do not necessarily need to intubate or insert LMA
-Bronchodilator
*Sympathetic stimulation
*Safe in asthma (no histamine release
*Last line treatment of status asthmaticus
-Increased salivation and bronchial secretions
*Use anti-sialogogue (anticholinergic like atropine or glycopyrrolate

82
Q

ketamine: other considerations

A

Causes postoperative nausea and vomiting (PONV)

May cause uterine contractions (1st trimester)

A drug of abuse (“Special K”, “Vitamin K”) due to its hallucinogenic effects

83
Q

ketamine indications

A

-Sick and unstable adults and children
-Burns surgery
-Debridement
-Change of dressings
-Short diagnostic procedures
-Analgesia
-Battlefield anaesthesia
-Status asthmaticus

84
Q

ketamine contraindications

A

-CVS pathology
*IHD, hypertension, AAA, CCF
-↑ ICP
-↑ IOP and “open eye”
-Psychiatric patients
-Epileptics
-Thyrotoxicosis
-Early pregnancy

85
Q

What receptors do benzodiazepines act on?

A

Benzodiazepines act on the GABA receptors.

86
Q

What is the main use of benzodiazepines in anaesthesia?

A

They are mainly used as sedatives for premedication and intra-operative sedation in anaesthesia.

rarely used as induction agents

87
Q

benzodiazepines: oral medication

A

Lorazepam, temazepam, diazepam, midazolam

88
Q

benzodiazepines

A

Midazolam

89
Q

What are the available preparations of midazolam?

A

Midazolam is available in 5 mg ampoules (1 mg/ml) and 15 mg ampoules (5 mg/ml).

90
Q

What are the concentrations of midazolam in the 5 mg and 15 mg ampoules?

A

The concentration of midazolam is 1 mg/ml in 5 mg ampoules and 5 mg/ml in 15 mg ampoules.

91
Q

What caution should be taken when checking midazolam ampoules?

A

Care should be taken when checking midazolam ampoules as the 5 mg and 15 mg ampoules may look identical.

92
Q

midazolam: pharmacokinetics

A

shorter duration of action

93
Q

midazolam dose

A

Premed: 0.5mg/kg
Adults 7.5-15mg orally
Works within 30 min
Kids – 0.25-0.5mg/kg PO

Induction: 0.1-0.3mg/kg

Sedation: 0.1mg/kg
Less with elderly

94
Q

midazolam: CNS

A

-Induction does not occur within 1 arm-brain circulation time
*Takes 55 - 140sec
-Anterograde amnesia
-Anxiolysis
-Sedation
-Prolonged recovery

95
Q

midazolam CVS

A

Stable
Often used in cardiac surgery

96
Q

midazolam Respiratory

A

Little effect

97
Q

midazolam GIT

A

Low incidence PONV

98
Q

midazolam UTERUS

A

Crosses placenta and cause floppy neonate

99
Q

Flumazenil

A

Specific benzodiazepine antagonist

100
Q

flumazenil

A

Dose: 0.2mg IV  short acting

101
Q

Total Intravenous Anaesthesia (TIVA)

A

Ideal: PROPOFOL
Ketamine

102
Q

TIVA: indications

A

-Risk of malignant hyperthermia
-Severe PONV in prior case
-Day-case surgery
-Cheaper than gases

103
Q

TIVA benefits

A

Rapid wake-up
No PONV

104
Q

TIVA requirements

A

infusion pumps

Anaesthesia (14 decks)

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